Between a float and a clear inside a wrapper with padding there is extra vertical space (the float and the clear have zero margins.)
The extra vertical space seems the same as the padding on the wrapper (above 10px, below 20px)
No padding on the wrapper, no extra space
The clear has hasLayout, no extra space
The clear is empty, extra space still there
There is something beside the float, no extra space
More floats. Horizontally resizing the window, different problems show up, See IE7-/Win: problems with a sequence of floats in a container.
The clear has hasLayout. No extra space, but the problems depending on window width remain.
Related bugs: